The radio frequency (RF) spectrum is a scarce and valuable commodity. In wireless networks, data traffic demands have increased rapidly, and are growing much faster than the availability of the spectrum. Since it is hard to allocate additional spectrum bandwidth for wireless broadband, spectrum sharing concepts have been introduced. Spectrum sharing includes situations where multiple users or multiple wireless applications are authorized to use the same range of frequencies on a non-exclusive basis. Spectrum sharing is used in different types of applications, ranging from commercial wireless applications to military applications.
Spectrum can be shared in several dimensions, including the time, frequency, and spatial (geographical) domain. In some applications, a primary system requires a protection zone/distance and sets an aggregate interference threshold to protect the system. An important component of spectrum sharing is “conditions” agreed upon between key stakeholders, including the primary spectrum user, licensee (e.g., the wireless carrier), and regulator (e.g., the Federal Communications Commission (FCC)). There are several ways for a licensee to achieve access to the shared spectrum that the primary system exclusively uses under these “conditions”. For example, a pilot warning beacon tone can be used at the primary system and a receiver can be used at the licensee device (or system) to monitor the presence of the pilot tone for accessing a shared frequency band. However, this implementation makes it difficult to detect and isolate interference among multiple spectrum users.
A reference signal may also be used to maintain a predetermined zone of protection for the primary system. For example, a licensee system may transmit the reference signal, such as a pilot signal, with a predetermined level of signal strength in defined frequency slots. The primary system measures the received signal strength of the reference signal and transmits this information back to the licensee system. The licensee system controls the traffic power levels such that they do not exceed the predetermined aggregate interference limit at the primary system.
However, this implementation requires protection zones for the primary system. Further, each protection zone is calculated on a per ground station (i.e., per system) basis. It may be impossible to accurately define the protection zone under all system deployment scenarios and varying RF environments by calculating an aggregate interference level. Also, even though a protection zone is set, there is no guarantee for the signal performance of the primary system.
Geolocation and timing information may also be used. For example, the shared spectrum is used by either the incumbent users or by the licensee in any given place at any given time. However, this requires pre-scheduling for sharing the band and applies restrictions on several dimensions (e.g., time, frequency, and spatial). Furthermore, this process does not always guarantee the signal performance of the primary system, and makes it difficult to detect and isolate interference among multiple spectrum users.
Thus, an alternative approach to spectrum sharing may be beneficial.